Active magnetic bearings are used to suspend shafts of rotating equipment subject to load spectra which vary with respect to time. Control of the position of the rotating assemblies of such equipment is effectuated by electromechanical systems which combine the use of feedback control and switching amplifiers such as voltage source inverters. Typically, the feedback control is based on an outer position control and an inner current control. The inner current control generates PWM (Pulse Width Modulation) signals to the switching amplifier which provides the desired currents as indicated by the outer position control.
For the practical application of such systems in industrial rotating machinery, the output of these amplifiers must vary in the order of thousands of cycles per second in order to maintain or adjust the desired position. Active magnetic bearings may e.g. be used in high speed rotation applications, especially in high power compressors for oil and gas applications.